Use of Series Resistors Adding a series
resistor greatly improves most uses of piezoelectric tweeters. Adding
about a 47 to 50 ohm or so resistor reduces the extreme treble response
by about 3 dB at 20 KHz, and by about 2 dB at 16 KHz. Lower treble frequencies
are less affected, but the effect is great enough to consider the sensitivity
reduced by 1 dB or maybe slightly more. If the effect is not enough to
tone down the "hissy" nature of most piezo tweeters, then use a slightly
higher value resistor. However, you should not have to go over 100 ohms,
since this has quite an effect on upper treble frequencies.

The KSN1025 tweeter and its relatives (including Radio Shack 40-1379)
have an internal resistor of 30-33 ohms. It may be good to add about 10
ohms to this. Please note that this model has about double the usual .15
or so uF of capacitance.

For general home stereo use, 1/2 watt resistors should work. For professional
duty applications, you need power resistors. This even means shorting
out the internal resistor in KSN1025 tweeters with a thin piece of wire
and using external power resistors.

One advantage of adding resistance is an increase in power handling and
reliability.

Use of Damping Material The back of piezo tweeters is
generally removable. This permits you to stuff in a bit of fiberglass
between the diaphragm and the ceramic piezo element, as well as behind
the ceramic piezo element. This somewhat damps down a "harsh" resonance
around the lowest frequencies that piezo tweeters work at.

With most models other than the KSN1025, you may need a bit of a trick
in order to put the tweeter back together. The trick is to solder thin
pieces of wire to the ceramic piezo element leads. There are holes in
the terminals on the back of the tweeter, although they may be filled
with solder. You can unplug the holes and thread the added wires through.

Use of Crossovers Although piezo tweeters are widely
used without crossovers, you will gain some power handling and reliability
if you remove frequencies out of their range. You may even slightly reduce
some of their upper midrange/lower treble harshness in the process.